This invention relates to a noise attenuation device for an air induction system, more particularly, the invention relates to a Helmholtz resonator for producing a forced response.
Internal combustion,engines produce undesirable induction noise which adversely affects the output torque and volumetric efficiency of the engine. The induction noise produced by the engine depends on the particular engine configuration and is affected by such factors as the number of cylinders, the volume and shape of the intake manifold plenum and intake runners, and other induction system parameters. The induction noise is caused by a pressure wave that travels away from the combustion chamber toward the inlet of the air induction system. The induction noise may be reduced and the engine performance improved by producing a wave traveling in: the direction of the combustion chamber 180xc2x0 out of phase of the noise wave. To this end, noise attenuation devices have been developed.
A Helmholtz resonator is one widely used noise attenuation device. The Helmholtz resonator produces a pressure wave that counteracts primary engine order noise waves, which have the greatest negative impact on engine performance. Helmholtz resonators typically provide a passive response targeted at a particular band width of noise. Because the Helmholtz resonator typically provides a passive response, losses occur which decrease the overall effectiveness of the resonator by producing a pressure wave having a narrower bandwidth and smaller amplitude than desired. Variable Helmholtz resonators have been developed, which vary the volume of the resonator to vary the band width at which the resonator attenuates noise. However, these variable resonators do not address the passive losses associated with the Helmholtz resonator. Accordingly, it is desirable to widen the band width of a Helmholtz resonator to further attenuate noise and increase the performance of the engine.
The present invention provides a Helmholtz resonator including a chamber at least partially defining a cavity. The chamber has a neck which defies a passage that is in fluid communication with the cavity. The chamber and the neck produce a passive response to a sound wave produced by the internal combustion engine. The sound wave negatively effects engine performance. An active resonator is disposed within the chamber. The active resonator produces a forced response for supplementing the passive response and increasing the band width of the noise attenuating pressure wave.
The Helmholtz resonator is in fluid communication with a portion of an air induction system that defines a passageway that carries the sound wave. A driver is connected to the active resonator, which is preferably a loud speaker, to drive the loud speaker and produce the forced response. The driver preferably utilizes a signal source, such as an engine speed signal, to synchronize the forced response with the engine speed. A phase compensator synchronizes the forced response with the sound wave, and an amplifier amplifies the signal to drive the loud speaker.
Accordingly, the present invention increases the band width of the passive response of the Helmholtz resonator to more effectively attenuate noise and increase engine performance.